This invention relates to a hydraulically releasable coupling device which serves to connect, releasably, coiled tubing and a subsea tool/subsea equipment etc., which coupling device exhibits an elongate body between two end coupling elements of the type with threaded pipe tan end and internally threaded pipe socket end, and which has a preferably central through bore, so that the body allows flow-through of drilling mud and other fluid, and comprises two sleeve-shaped parts held together by means of releasable locking/blocking means, whose blocking effect may be brought to an end through intentional hydraulic release of the coupling device comprising a radially expandable locking ring, which normally prevents relative movement of the sleeve-shaped parts of the elongate body of the coupling device.
The Norwegian publication No. 180 552 discloses a hydraulically releasable coupling device of the kind initially mentioned, wherein two end pieces are connected by said radially expandable locking ring, in its normal operative position (in which release/disconnection is not relevant), being engaged in grooves in a securing sleeve incorporated in the coupling device. An axially displaceable securing sleeve encloses the locking ring by its one end portion, and prevents it from expanding radially, thereby unintentionally causing tools to be released and disconnected from the coiled tubing. An intentional release, which is brought about hydraulically, is only to be effected if the tool has become jammed and is immovably stuck.
By the known coupling device according to Norwegian publication No. 180.552, said securing sleeve is retained by means of shear pins until release is desirable or necessary. When the coupling device is to be released hydraulically, a ball-like sealing body is positioned, in a manner known in itself, on an internal seat of a piston sleeve included in the coupling device, so that fluid flow through the tubular coupling device is prevented, and pressure builds up upstream of the sealing body. Increasing hydraulic force acting on the sealing body and the seat-carrying piston sleeve, forces the piston sleeve against the securing sleeve so that the shear pins break, and the securing sleeve is displaced, whereby it no longer encloses the locking ring. Said grooves of the securing sleeve are provided with sloping flanks, and the axial force acting on the locking ring through the through passage of the coupling device, gives rise, due to said slope, to a radial force, which brings the locking ring to expand radially and release the locking sleeve.
By the release of such a hydraulically activatable coupling device, it is divided into at least two separate parts, one of which is securely connected to the tool/equipment which has become stuck at the point of its operations, whereas the second part is firmly screwed to the end of the coiled tubing and follows this on the hauling thereof into a surface position. Later is decided whether the tool/equipment should be retrieved, drilled to pieces where it is or similar, but this is not an object of the present invention and is consequently not described in further detail.
The above mentioned, known hydraulically releasable coupling device comprises a constructively rather complex structure of quite a few movable parts. However, this drawback is fairly limited relative to the tendency of releasing on the occurrence of high fluid pressures, which can occur suddenly.
This fluid-pressure-dependent undesirable tendency of this known coupling device is the more disadvantageous, considered on the basis that in down-hole operations it is often desirable to work by high fluid pressure. Of course, this needs to be carried out without the risk that the coupling device releases, and the elongate sleeve-shaped body is divided into two separate parts, of which only one can follow the coiled tubing up in a highly undesirable interruption of operation/hauling operation, whereby the tool/equipment itself remains in the downhole position in which the work operations were unintentionally interrupted by a hydraulic releasing (high fluid pressure) of the coupling device. The tool/equipment may be retrieved by a so-called fishing operation, or it may be drilled through and rendered harmless in its position downhole.
Before work operations are resumed after such unpredicted undesirable interruptions, valuable time has normally been lost.
In one embodiment, the invention comprises a hydraulically releasable coupling device including an upstream part arranged to permit connection to tubing and a downstream part arranged to be connected to a tool or equipment. The coupling device also includes a radially expandable locking ring configured to expand and thereby to disconnect the coupling device, a movable securing ring portion enclosing the locking ring at least partially in an unexpanded locking position thereof; and a piston body connected to the securing ring portion and having a through passage which is provided downstream with a restriction element.